There is a technology for detecting a moving body that appears in an image produced by a camera installed at a fixed position, such as, a fixed-point camera. However, the technology is confronted with a problem that it is hard to detect a moving body from an image produced by a camera mounted on a moving body such as a human being or vehicle.
There is a technology for detecting a moving body by producing feature points, which are matched with each other, from two frames produced by a monocular camera. Unless the matched feature points meet a condition of epipolar geometry or constraint, the feature points are detected as a moving body.
In the technology, as long as a camera whose exposure time is short (that is, frame rate is high) is used, a searching range for feature points that are matched with each other can be narrowed down. However, when the exposure time is short, since information on a moving body is produced from discontinuous photographic images, it is hard to accurately follow the trajectory of the moving body, and precision in detecting the moving body is insufficient.
In contrast, when a camera whose exposure time is long (that is, frame rate is low) is used, since a moving distance of a subject or camera gets longer, a searching range for feature points that are matched with each other is widened. When the searching range is widened, precision in detecting a moving body gets lower than that when a camera whose exposure time is short is used. In addition, occlusion in which the moving body does not appear in a photographic image because the moving body is hidden behind a body existing in front of (on the side of the camera) the moving body is liable to occur. This poses a problem in that precision in detecting the moving body is further degraded.